Journal articles: 'Classical gravity'

1

Novozhilov, Yu V., and D. V. Vassilevich. "Induced classical gravity." Letters in Mathematical Physics 21, no. 3 (March 1991): 253–71. http://dx.doi.org/10.1007/bf00420376.

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2

Drechsler, Wolfgang. "Classical versus quantum gravity." Foundations of Physics 23, no. 2 (February 1993): 261–76. http://dx.doi.org/10.1007/bf01883629.

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Struyve, Ward. "Semi-classical approximations based on Bohmian mechanics." International Journal of Modern Physics A 35, no. 14 (May 20, 2020): 2050070. http://dx.doi.org/10.1142/s0217751x20500700.

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Semi-classical theories are approximations to quantum theory that treat some degrees of freedom classically and others quantum mechanically. In the usual approach, the quantum degrees of freedom are described by a wave function which evolves according to some Schrödinger equation with a Hamiltonian that depends on the classical degrees of freedom. The classical degrees of freedom satisfy classical equations that depend on the expectation values of quantum operators. In this paper, we study an alternative approach based on Bohmian mechanics. In Bohmian mechanics the quantum system is not only described by the wave function, but also with additional variables such as particle positions or fields. By letting the classical equations of motion depend on these variables, rather than the quantum expectation values, a semi-classical approximation is obtained that is closer to the exact quantum results than the usual approach. We discuss the Bohmian semi-classical approximation in various contexts, such as nonrelativistic quantum mechanics, quantum electrodynamics and quantum gravity. The main motivation comes from quantum gravity. The quest for a quantum theory for gravity is still going on. Therefore a semi-classical approach where gravity is treated classically may be an approximation that already captures some quantum gravitational aspects. The Bohmian semi-classical theories will be derived from the full Bohmian theories. In the case there are gauge symmetries, like in quantum electrodynamics or quantum gravity, special care is required. In order to derive a consistent semi-classical theory it will be necessary to isolate gauge-independent dependent degrees of freedom from gauge degrees of freedom and consider the approximation where some of the former are considered classical.

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4

KAZAKOV, KIRILL A. "CLASSICAL SCALE OF QUANTUM GRAVITY." International Journal of Modern Physics D 12, no. 09 (October 2003): 1715–19. http://dx.doi.org/10.1142/s0218271803004110.

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Characteristic length scale of the post-Newtonian corrections to the gravitational field of a body is given by its gravitational radius r g . The role of this scale in quantum domain is discussed in the context of the low-energy effective theory. The question of whether quantum gravity effects appear already at r g leads to the question of correspondence between classical and quantum theories, which in turn can be unambiguously resolved by considering the issue of general covariance. The O(ℏ0) loop contributions turn out to violate the principle of general covariance, thus revealing their essentially quantum nature. The violation is O(1/N), where N is the number of particles in the body. This leads naturally to a macroscopic formulation of the correspondence principle.

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Jalalzadeh, S., M. Mehrnia, and H. R. Sepangi. "Classical tests in brane gravity." Classical and Quantum Gravity 26, no. 15 (July 10, 2009): 155007. http://dx.doi.org/10.1088/0264-9381/26/15/155007.

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6

Marugan, G. A. M. "Lovelock gravity and classical wormholes." Classical and Quantum Gravity 8, no. 5 (May 5, 1991): 935–46. http://dx.doi.org/10.1088/0264-9381/8/5/017.

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7

Suranyi, P., and L. C. R. Wijewardhana. "Classical instability in Lovelock gravity." Journal of Physics: Conference Series 343 (February 8, 2012): 012118. http://dx.doi.org/10.1088/1742-6596/343/1/012118.

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8

Mannheim, Philip D. "Open questions in classical gravity." Foundations of Physics 24, no. 4 (April 1994): 487–511. http://dx.doi.org/10.1007/bf02058060.

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9

Tameike, S. "Classical Gravity and Fiber Bundles." Progress of Theoretical Physics 100, no. 6 (December 1, 1998): 1159–79. http://dx.doi.org/10.1143/ptp.100.1159.

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10

Kim, Sang Pyo. "Classical spacetime from quantum gravity." Classical and Quantum Gravity 13, no. 6 (June 1, 1996): 1377–82. http://dx.doi.org/10.1088/0264-9381/13/6/011.

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11

Calheiros, A., and M. D. Maia. "Classical gravity in two dimensions." Physics Letters A 136, no. 4-5 (April 1989): 193–96. http://dx.doi.org/10.1016/0375-9601(89)90559-8.

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12

BERGSHOEFF, E., C. N. POPE, L. J. ROMANS, E. SEZGIN, and X. SHEN. "W∞ GRAVITY AND SUPER-W∞ GRAVITY." Modern Physics Letters A 05, no. 24 (September 30, 1990): 1957–66. http://dx.doi.org/10.1142/s0217732390002237.

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13

Dehnen, H., and F. Ghaboussi. "Central force bremsstrahlung in classical gravity." Classical and Quantum Gravity 2, no. 6 (November 1, 1985): L141—L143. http://dx.doi.org/10.1088/0264-9381/2/6/006.

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14

Madore, J., and J. Mourad. "Quantum space–time and classical gravity." Journal of Mathematical Physics 39, no. 1 (January 1998): 423–42. http://dx.doi.org/10.1063/1.532328.

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15

Madore, J. "Classical gravity on fuzzy space-time." Nuclear Physics B - Proceedings Supplements 56, no. 3 (July 1997): 183–90. http://dx.doi.org/10.1016/s0920-5632(97)00325-3.

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16

Schutz, Bernard F. "From Classical Theory to Quantum Gravity." Space Science Reviews 148, no. 1-4 (December 2009): 15–23. http://dx.doi.org/10.1007/s11214-009-9575-9.

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17

Schoutens, K., A. Sevrin, and P. van Nieuwenhuizen. "Covariant formulation of classical W-gravity." Nuclear Physics B 349, no. 3 (February 1991): 791–814. http://dx.doi.org/10.1016/0550-3213(91)90398-h.

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18

Schwarz, Patricia M. "Gravity waves in classical string theory." Nuclear Physics B 373, no. 2 (April 1992): 529–56. http://dx.doi.org/10.1016/0550-3213(92)90443-f.

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19

Mazzitelli, Francisco D., and Noureddine Mohammedi. "Classical gravity coupled to Liouville theory." Nuclear Physics B 401, no. 1-2 (July 1993): 239–56. http://dx.doi.org/10.1016/0550-3213(93)90304-8.

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20

Ajabshirizadeh, A., A. Jahan, and B. Nadiri Niri. "Classical gravitational bremsstrahlung in R2-gravity." Modern Physics Letters A 29, no. 28 (September 14, 2014): 1450145. http://dx.doi.org/10.1142/s0217732314501454.

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The R2-gravity contribution to the gravitational energy loss in a classical scattering of two charged particles is calculated using the classical formula of the quadrupole radiation, assuming the small angle scattering approximation.

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21

Doplicher, Sergio, Klaus Fredenhagen, and John E. Roberts. "Spacetime quantization induced by classical gravity." Physics Letters B 331, no. 1-2 (June 1994): 39–44. http://dx.doi.org/10.1016/0370-2693(94)90940-7.

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22

HA, YUAN K. "SEVERE CHALLENGES IN GRAVITY THEORIES." International Journal of Modern Physics: Conference Series 07 (January 2012): 219–26. http://dx.doi.org/10.1142/s2010194512004291.

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Gravity is specifically the attractive force between two masses separated at a distance. Is this force a derived or a fundamental interaction? We believe that all fundamental interactions are quantum in nature but a derived interaction may be classical. Severe challenges have appeared in many quantum theories of gravity. None of these theories has thus far attained its goal in quantizing gravity and some have met remarkable defeat. We are led to ponder whether gravitation is intrinsically classical and that there would exist a deeper and structurally different underlying theory which would give rise to classical gravitation, in the sense that statistical mechanics, quantum or classical, provides the underlying theory of classical thermodynamics.

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23

AMELINO-CAMELIA, GIOVANNI. "DIMENSIONFUL DEFORMATIONS OF POINCARÉ SYMMETRIES FOR A QUANTUM GRAVITY WITHOUT IDEAL OBSERVERS." Modern Physics Letters A 13, no. 16 (May 30, 1998): 1319–25. http://dx.doi.org/10.1142/s0217732398001376.

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Quantum mechanics is revisited as the appropriate theoretical framework for the description of the outcome of experiments that rely on the use of classical devices. In particular, it is emphasized that the limitations on the measurability of (pairs of conjugate) observables encoded in the formalism of quantum mechanics reproduce faithfully the "classical-device limit" of the corresponding limitations encountered in (real or gedanken) experimental setups. It is then argued that devices cannot behave classically in quantum gravity, and that this might raise serious problems for the search of a class of experiments described by theories obtained by "applying quantum mechanics to gravity." It is also observed that using heuristic/intuitive arguments based on the absence of classical devices one is led to consider some candidate quantum gravity phenomena involving dimensionful deformations of the Poincaré symmetries.

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24

Klauder, John R. "An Ultralocal Classical and Quantum Gravity Theory." Journal of High Energy Physics, Gravitation and Cosmology 06, no. 04 (2020): 656–61. http://dx.doi.org/10.4236/jhepgc.2020.64044.

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25

Klauder, John R. "The Unification of Classical and Quantum Gravity." Journal of High Energy Physics, Gravitation and Cosmology 07, no. 01 (2021): 88–97. http://dx.doi.org/10.4236/jhepgc.2021.71004.

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26

Hameeda, Mir, Angelo Plastino, Mario Carlos Rocca, and Javier Zamora. "Classical Partition Function for Non-Relativistic Gravity." Axioms 10, no. 2 (June 16, 2021): 121. http://dx.doi.org/10.3390/axioms10020121.

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We considered the canonical gravitational partition function Z associated to the classical Boltzmann–Gibbs (BG) distribution e−βHZ. It is popularly thought that it cannot be built up because the integral involved in constructing Z diverges at the origin. Contrariwise, it was shown in (Physica A 497 (2018) 310), by appeal to sophisticated mathematics developed in the second half of the last century, that this is not so. Z can indeed be computed by recourse to (A) the analytical extension treatments of Gradshteyn and Rizhik and Guelfand and Shilov, that permit tackling some divergent integrals and (B) the dimensional regularization approach. Only one special instance was discussed in the above reference. In this work, we obtain the classical partition function for Newton’s gravity in the four cases that immediately come to mind.

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27

Calcagni, Gianluca. "Classical and quantum gravity with fractional operators." Classical and Quantum Gravity 38, no. 16 (July 22, 2021): 165005. http://dx.doi.org/10.1088/1361-6382/ac1081.

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28

Gambini, Rodolfo, Esteban Mato, Javier Olmedo, and Jorge Pullin. "Classical axisymmetric gravity in real Ashtekar variables." Classical and Quantum Gravity 36, no. 12 (May 29, 2019): 125009. http://dx.doi.org/10.1088/1361-6382/ab1d82.

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29

Ashtekar, Abhay. "New Variables for Classical and Quantum Gravity." Physical Review Letters 57, no. 18 (November 3, 1986): 2244–47. http://dx.doi.org/10.1103/physrevlett.57.2244.

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30

Kalligas, D., P. S. Wesson, and C. W. F. Everitt. "The classical tests in Kaluza-Klein gravity." Astrophysical Journal 439 (February 1995): 548. http://dx.doi.org/10.1086/175195.

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31

Schmidt, Hans-Jurgen. "The Classical Solutions of Two-dimensional Gravity." General Relativity and Gravitation 31, no. 8 (August 1999): 1187–210. http://dx.doi.org/10.1023/a:1026708320831.

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32

Eingorn, Maxim, and Alexander Zhuk. "Classical tests of multidimensional gravity: negative result." Classical and Quantum Gravity 27, no. 20 (September 14, 2010): 205014. http://dx.doi.org/10.1088/0264-9381/27/20/205014.

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33

Horowitz, G. T. "Topology change in classical and quantum gravity." Classical and Quantum Gravity 8, no. 4 (April 1, 1991): 587–601. http://dx.doi.org/10.1088/0264-9381/8/4/007.

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34

Gasperini, M. "Classical repulsive gravity and broken Lorentz symmetry." Physical Review D 34, no. 8 (October 15, 1986): 2260–62. http://dx.doi.org/10.1103/physrevd.34.2260.

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35

Hendi, Seyed Hossein, Christian Corda, S. Habib Mazharimousavi, Davood Momeni, Masoud Sepehri-Rad, and Emmanuel N. Saridakis. "Classical and Quantum Gravity and Its Applications." Advances in High Energy Physics 2017 (2017): 1–2. http://dx.doi.org/10.1155/2017/9736761.

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36

Benedetti, Riccardo, and Enore Guadagnini. "Classical Teichmüller theory and (2+1) gravity." Physics Letters B 441, no. 1-4 (November 1998): 60–68. http://dx.doi.org/10.1016/s0370-2693(98)01156-3.

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37

Arbuzova, E. V., A. D. Dolgov, and L. Reverberi. "Jeans instability in classical and modified gravity." Physics Letters B 739 (December 2014): 279–84. http://dx.doi.org/10.1016/j.physletb.2014.11.004.

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38

HU, B. L. "GRAVITY AND NONEQUILIBRIUM THERMODYNAMICS OF CLASSICAL MATTER." International Journal of Modern Physics D 20, no. 05 (May 20, 2011): 697–716. http://dx.doi.org/10.1142/s0218271811019049.

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39

Clément, Gérard. "Classical solutions in three-dimensional cosmological gravity." Physical Review D 49, no. 10 (May 15, 1994): 5131–34. http://dx.doi.org/10.1103/physrevd.49.5131.

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40

Pons, J. M., D. C. Salisbury, and K. A. Sundermeyer. "Observables in classical canonical gravity: Folklore demystified." Journal of Physics: Conference Series 222 (April 1, 2010): 012018. http://dx.doi.org/10.1088/1742-6596/222/1/012018.

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41

Brout, R. "Time and temperature in semi-classical gravity." Zeitschrift f�r Physik B Condensed Matter 68, no. 2-3 (June 1987): 339–41. http://dx.doi.org/10.1007/bf01304250.

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42

Paunković, Nikola, and Marko Vojinović. "Equivalence Principle in Classical and Quantum Gravity." Universe 8, no. 11 (November 12, 2022): 598. http://dx.doi.org/10.3390/universe8110598.

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We give a general overview of various flavours of the equivalence principle in classical and quantum physics, with special emphasis on the so-called weak equivalence principle, and contrast its validity in mechanics versus field theory. We also discuss its generalisation to a theory of quantum gravity. Our analysis suggests that only the strong equivalence principle can be considered fundamental enough to be generalised to a quantum gravity context since all other flavours of equivalence principle hold only approximately already at the classical level.

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43

Oda, Ichiro. "Schwarzschild solution from Weyl transverse gravity." Modern Physics Letters A 32, no. 03 (January 11, 2017): 1750022. http://dx.doi.org/10.1142/s0217732317500225.

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We study classical solutions in the Weyl-transverse (WTDiff) gravity. The WTDiff gravity is invariant under both the local Weyl (conformal) transformation and the volume preserving diffeomorphisms (Diff) (transverse diffeomorphisms (TDiff)) and is known to be equivalent to general relativity at least at the classical level. In particular, we find that in a general spacetime dimension, the Schwarzschild metric is a classical solution in the WTDiff gravity when it is expressed in the Cartesian coordinate system.

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44

HORWITZ, GERALD. "TIME AND ENTROPY FROM SEMI-CLASSICAL TUNNELING OF THE COSMOLOGICAL SCALE FUNCTION." International Journal of Modern Physics D 05, no. 06 (December 1996): 885–902. http://dx.doi.org/10.1142/s0218271896000539.

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Two major apparently unrelated problems, that of the origin of time in the universe associated with quantum gravity and of the entropy in de Sitter cosmological models, are found to have their origin in a single physical phenomenon: the semi-classical tunneling through a classically forbidden region of the cosmological scale factor. In this region there is a mixing of the states of quantum matter and those of the semi-classical gravity which produces a thermal mixture of the matter states and hence an “entropy;” this same mixing effect brings about the conversion of a parametric time variable into a physical intrinsic time.

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45

De, Shounak, Tejinder P. Singh, and Abhinav Varma. "Quantum gravity as an emergent phenomenon." International Journal of Modern Physics D 28, no. 14 (October 2019): 1944003. http://dx.doi.org/10.1142/s0218271819440036.

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There ought to exist a reformulation of quantum theory which does not depend on classical time. To achieve such a reformulation, we introduce the concept of an atom of space-time-matter (STM). An STM atom is a classical noncommutative geometry (NCG), based on an asymmetric metric, and sourced by a closed string. Different such atoms interact via entanglement. The statistical thermodynamics of a large number of such atoms gives rise, at equilibrium, to a theory of quantum gravity. Far from equilibrium, where statistical fluctuations are large, the emergent theory reduces to classical general relativity. In this theory, classical black holes are far from equilibrium low entropy states, and their Hawking evaporation represents an attempt to return to the [maximum entropy] equilibrium quantum gravitational state.

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46

Ashoorioon, Amjad, P. S. Bhupal Dev, and Anupam Mazumdar. "Implications of purely classical gravity for inflationary tensor modes." Modern Physics Letters A 29, no. 30 (September 28, 2014): 1450163. http://dx.doi.org/10.1142/s0217732314501636.

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We discuss the implications of a purely classical (instead of quantum) theory of gravity for the primordial gravitational wave spectrum generated during inflation. We argue that for a scalar field driven inflation in a classical gravity the amplitude of the gravitational wave will be too small, irrespective of its primordial seed, to be detected in any forthcoming experiments. Therefore, a positive detection of the B-mode polarizations in the Cosmic Microwave Background (CMB) spectrum will naturally confirm the quantum nature of gravity itself. Furthermore there will be no upper limit on the scale of inflation in the case of classical gravity, and a high-scale model of inflation can easily bypass the observational constraints.

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47

Engelhardt, Netta, and Gary T. Horowitz. "New insights into quantum gravity from gauge/gravity duality." International Journal of Modern Physics D 25, no. 12 (October 2016): 1643002. http://dx.doi.org/10.1142/s0218271816430021.

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Using gauge/gravity duality, we deduce several nontrivial consequences of quantum gravity from simple properties of the dual field theory. These include: (1) a version of cosmic censorship, (2) restrictions on evolution through black hole singularities, and (3) the exclusion of certain cosmological bounces. In the classical limit, the latter implies a new singularity theorem.

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48

Sturani, Riccardo. "Fundamental Gravity and Gravitational Waves." Symmetry 13, no. 12 (December 10, 2021): 2384. http://dx.doi.org/10.3390/sym13122384.

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While being as old as general relativity itself, the gravitational two-body problem has never been under so intense investigation as it is today, spurred by both phenomenological and theoretical motivations. The observations of gravitational waves emitted by compact binary coalescences bear the imprint of the source dynamics, and as the sensitivity of detectors improve over years, more accurate modeling is being required. The analytic modeling of classical gravitational dynamics has been enriched in this century by powerful methods borrowed from field theory. Despite being originally developed in the context of fundamental particle quantum scatterings, their applications to classical, bound system problems have shown that many features usually associated with quantum field theory, such as, e.g., divergences and counterterms, renormalization group, loop expansion, and Feynman diagrams, have only to do with field theory, be it quantum or classical. The aim of this work is to present an overview of this approach, which models massive astrophysical objects as nonrelativistic particles and their gravitational interactions via classical field theory, being well aware that while the introductory material in the present article is meant to represent a solid background for newcomers in the field, the results reviewed here will soon become obsolete, as this field is undergoing rapid development.

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49

Chiarelli, Piero. "The Gravity of the Classical Klein-Gordon Field." Symmetry 11, no. 3 (March 4, 2019): 322. http://dx.doi.org/10.3390/sym11030322.

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The work shows that the evolution of the field of the free Klein–Gordon equation (KGE), in the hydrodynamic representation, can be represented by the motion of a mass density ∝ | ψ | 2 subject to the Bohm-type quantum potential, whose equation can be derived by a minimum action principle. Once the quantum hydrodynamic motion equations have been covariantly extended to the curved space-time, the gravity equation (GE), determining the geometry of the space-time, is obtained by minimizing the overall action comprehending the gravitational field. The derived Einstein-like gravity for the KGE field shows an energy-impulse tensor density (EITD) that is a function of the field with the spontaneous emergence of the “cosmological” pressure tensor density (CPTD) that in the classical limit leads to the cosmological constant (CC). The energy-impulse tensor of the theory shows analogies with the modified Brans–Dick gravity with an effective gravity constant G divided by the field squared. Even if the classical cosmological constant is set to zero, the model shows the emergence of a theory-derived quantum CPTD that, in principle, allows to have a stable quantum vacuum (out of the collapsed branched polymer phase) without postulating a non-zero classical CC. In the classical macroscopic limit, the gravity equation of the KGE field leads to the Einstein equation. Moreover, if the boson field of the photon is considered, the EITD correctly leads to its electromagnetic energy-impulse tensor density. The work shows that the cosmological constant can be considered as a second order correction to the Newtonian gravity. The outputs of the theory show that the expectation value of the CPTD is independent by the zero-point vacuum energy density and that it takes contribution only from the space where the mass is localized (and the space-time is curvilinear) while tending to zero as the space-time approaches to the flat vacuum, leading to an overall cosmological effect on the motion of the galaxies that may possibly be compatible with the astronomical observations.

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50

Chiarelli, Piero. "The Spinor-Tensor Gravity of the Classical Dirac Field." Symmetry 12, no. 7 (July 6, 2020): 1124. http://dx.doi.org/10.3390/sym12071124.

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In this work, with the help of the quantum hydrodynamic formalism, the gravitational equation associated with the classical Dirac field is derived. The hydrodynamic representation of the Dirac equation described by the evolution of four mass densities, subject to the theory-defined quantum potential, has been generalized to the curved space-time in the covariant form. Thence, the metric of space-time has been defined by imposing the minimum action principle. The derived gravity shows the spontaneous emergence of the “cosmological” gravity tensor (CGT), a generalization of the classical cosmological constant (CC), as a part of the energy-impulse tensor density (EITD). Even if the classical cosmological constant is set to zero, the CGT is non-zero, allowing a stable quantum vacuum (out of the collapsed branched polymer phase). The theory shows that in the classical macroscopic limit, the general relativity equation is recovered. In the perturbative approach, the CGT leads to a second-order correction to Newtonian gravity that takes contribution from the space where the mass is localized (and the space-time is curvilinear), while it tends to zero as the space-time approaches the flat vacuum, leading, as a means, to an overall cosmological constant that may possibly be compatible with the astronomical observations. The Dirac field gravity shows analogies with the modified Brans–Dicke gravity, where each spinor term brings an effective gravity constant G divided by its field squared. The work shows that in order to obtain the classical minimum action principle and the general relativity limit of the macroscopic classical scale, quantum decoherence is necessary.

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Journal articles on the topic 'Classical gravity'

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